The present invention relates to an ultrasonic diagnostic equipment and, more particularly, to the one of linear electronic scanning type for electronically moving in parallel the ultrasonic beam.
An ultrasonic scanning type diagnostic equipment has a plurality of ultrasonic transducers. Any selected one of the transducers emits an ultrasonic beam to a living body. The equipment receives pulses reflected from the living body and displays an image of the living body based on the reflected pulses. Such an equipment is disclosed in U.S. Pat. Nos. 3,789,833 and 3,881,466. The specifications of these U.S. patents, however, do not describe in detail a scanning circuit for driving and switching the ultrasonic transducers of the equipment. In the conventional linear electronic scanning type diagnostic equipment, the ultransonic transducers are switched on and off one after another. To drive any one of the transducers a switching circuit is employed to control not only the voltage of the pulses reflected from a living body but also the voltage of the input pulses to the transducer.
Generally, input pulses to drive an utlrasonic transducer have a relatively high voltage, e.g. tens to hundreds of volts. A switching circuit applied with such a high voltage will inevitably generate pulses each time it is operated. The unnecessary ultrasonic pulses thus produced will result in a virtual or ghost image of the living body. Of course, the switching circuit is made to withstand a high voltage and a great current. As a result, it cannot detect input signals at the best possible signal/noise (S/N) ratio. Such a switching circuit is indispensable to the conventional ultrasonic scanning type diagnostic equipment. This is why the equipment has a complicated circuit construction and is very costly.